Thoracic outlet syndrome (TOS) is an umbrella term for conditions involving the compression of neurovascular structures (e.g., the brachial plexus or the subclavian artery or vein) as they pass from the lower neck to the armpit. Causes include trauma, tumors, or the presence of a cervical rib. Neurogenic TOS is the most common type and involves the compression of the brachial plexus, leading to neck pain and numbness and tingling in the fingers. Arterial TOS involves compression of the subclavian artery and presents with pain, pallor, coldness, and pulselessness in the affected arm, especially during overhead activities. Venous TOS results in pain, cyanosis, and swelling of the arm. Imaging techniques such as duplex sonography, X-ray, MRI, or electrodiagnostic testing are used to detect the cause of TOS. Mild symptoms should be treated with pain medication and physical therapy. Surgical resection of the causal structures might become necessary in the case of progressive neurologic dysfunction or acute vascular insufficiency.
Compression of subclavian vessels and the lower trunk of the brachial plexus (mainly occurs within the scalene triangle) due to:
- Physical trauma (e.g. hyperextension neck injuries)
- Repetitive motion of the abducted and externally rotated shoulder; (e.g., tennis, baseball, swimming, repetitive throwing, carrying heavy objects overhead)
- Structural abnormalities
Clinical features of TOS depend on the anatomic structure affected by compression and are more pronounced during and after overhead activity.
- Compression of parts of the brachial plexus (95% of cases) 
- Compression of the subclavian vein (up to 3% of cases) 
- Compression of the subclavian artery (< 1% of cases) 
Swelling and venous distention in the arm may be a sign of venous thrombosis of the arm.
- Definition: a provocation test that is used to reproduce symptoms of TOS
- The patient sits in a relaxed position while the examiner palpates the radial pulse.
Passive abduction of 90° and lateral rotation and extension of the arm
- The effect may be amplified by asking the patient to extend their head and rotate it to the affected side while breathing in deeply.
- This maneuver causes contraction of the anterior and middle scalene muscles, which narrows the posterior scalene gap, causing compression of the subclavian artery and the brachial plexus, with subsequent loss of the radial pulse or paresthesia in the case of arterial or neurogenic TOS.
- Definition: a provocation test used to reproduce paresthesia and changes in the radial pulse by performing the following maneuvers
Roos stress test
- Definition: a provocation test used to reproduce symptoms of TOS
- Maneuver: Both shoulders are positioned in abduction and are externally rotated at 90° angles, with elbows flexed at 90°, while the patient repeatedly makes a fist and then relaxes the hand.
- Positive: sensation of heaviness or fatigue in affected limb
- Negative: no change in sensation
- Radiographs of the spine, shoulder, collarbone might show bony abnormalities
- CT or MRI imaging mainly to exclude other conditions that manifest similarly (e.g., , , cervical disc disorders, )
- Mild cases
- Thoracic outlet decompression surgery: in cases of acute vascular insufficiency or progressive neurologic dysfunction or if conservative treatment fails